Control of posture

Question 1

Postural control

Answer 1

• Maintenance of body orientation and stability (balance) of body segments
• Postural orientation can be defined as “the relationship of body segments to each other, to the task, and to the environment”
• Maintenance of postural stability or center of mass within base of support while standing or sitting still, when the base of support does not change.

Question 2

Postural control - 2

Answer 2

• The ability to regain postural stability after external stimulus or perturbation, with or without a change in base of support
• The ability to maintain and regain postural stability after self-initiated movements

Question 3

COM

Answer 3

• Normal erect posture characterized by small anterior posterior, and medial lateral oscillations over a fixed base of support
• A bodies centre of mass (COM represents the mean position of the matter in a body or system) is typically just anterior to the S1 vertebrae

Question 4

during quiet erect standing

Answer 4

In quiet erect standing, the body’s COM passes very close to the ear, slightly anterior to the acromion process of the scapula, close to the greater trochanter, slightly anterior to the knee joint, and anterior to the ankle joint

Question 5

Centre of Pressure (COP)

Answer 5

A bodies centre of pressure (COP) represents a single point on a surface through which the resultant force passes.
This is within the “foot print” during quiet stance.
COP fluctuates during quiet standing with our body sway

Question 6

Aging

Answer 6

Postural sway is increases with age

• Some association with COP increase and occurrence of retrospective falls and prospective falls
• Changes in sensory information (input), and motor ability (output)

Question 7

Sensory inputs to the postural control system include:

Answer 7

VISUAL
Lighting; movement of self or environment
VESTIBULAR
Gravity; Linear & Angular Head and Eye Movement
SOMATOSENSORY
Proprioception and tactile. Surface changes & irregularities; Base of support changes

Question 8

CNS

Answer 8

CNS selects and weights inputs based upon: Availability, Accuracy, Value to task

• These multisensory inputs can elicit quick changes in posture.
• Particularly when the brain predicts sensory inputs, but received different information.
• CNS corrects the body’s motion based on the error between the predicted and actual sensory inputs. Fast processing power… Also long term adaptations….

Question 9

How is postural control maintained?

Answer 9

Postures are maintained by a combination of active (muscle contraction) and passive structures (primarily connective tissue including within musculotendinous units)

• We learn through exposure how to prepare and respond to external and internal perturbations

Question 10

Our postural control system must respond to (or prepare for):
Externally generated stimuli/perturbations:

Answer 10

Externally generated stimuli/perturbations:
Constant (or longer term) environmental forces: e.g. Gravity, merry-go-round!
Occasional environmentally generated forces:
e.g. Ground reaction forces, being pushed / support being removed,
catching/hitting a ball.

Question 11

Our postural control system must respond to (or prepare for): 
Internally generated (self initiated) stimuli/perturbations:

Answer 11

Internally generated (self initiated) stimuli/perturbations:
Rhythmical internally generated forces e.g. Breathing, gait
Occasional internally generated forces
e.g. Coughing/laughing, preparing to catch a ball

Question 12

cerebellum

Answer 12

• The cerebellum contributes to coordination, precision, timing and refining movement.
• It receives and integrates sensory input, and cortical input (the motor plan), and fine-tunes motor activity.

Question 13

Cerebellum refining movement

Answer 13

• Refining movement: by comparing the motor plan to sensory input, elicit both short term and long term changes in the plan

Question 14

Cerebellar damage is associated with disorders of:

Answer 14

Voluntary movements:
Short term: Errors in force, direction, speed of movement Longer term: “Motor learning”, refining movement over time
Postural control: Balance
Gait pattern, wide stance Hypotonia (decreased muscle tone)

Question 15

Corticospinal tracts

Answer 15

• UMN within the corticospinal tract connect to LMN’s, and control movement of the torso, upper and lower limbs.
• UMN from the corticospinal tract divide into those from the lateral and anterior corticospinal tracts.
• UMN from the lateral corticospinal tract transmit the neural signal to produce voluntary movements of the distal extremities.
• UMN from the anterior corticospinal tract are responsible for postural adjustments that occur to compensate for voluntary movements.

Question 16

Motor Neurons

Answer 16

• Upper motor neurons (UMNs) refer to all motoneurons that arise from cortex and brainstem that influence the activity of - lower motoneurons (LMN).
  Lower motor neurons (LMN) originate in the spinal cord.

Question 17

Corticobulbar tracts

Answer 17

Corticobulbar UMN primarily originate from M1

• Indirect connections (polysynaptic) between cortex and LMN via the basal ganglia, cerebellum and brainstem nuclei
• Interaction with sensory information, refines the descending signal.
• Other UMN (eg from the vestibulospinal tracts) initiate postural adjustments in response to changes in balance
• Facilitates the maintenance of balance and posture